1. Field of the Invention
The present invention relates to a system for managing data for using, i.e., storing, copying, editing, or transferring digital data content.
2. Background Art
Because analog data content is deteriorated in quality whenever storing, copying, editing, or transferring it, controlling copyrights associated with these operations has not been a serious problem. However, because digital data content is not deteriorated in quality after repeatedly storing, copying, editing, or transferring it, controlling copyrights associated with these operations for digital data content is a serious problem.
Because there has been hitherto no adequate method for controlling a copyright for digital data content, the copyright is handled by the copyright law or contracts. Even in the copyright law, compensation money for a digital-type sound- or picture-recorder is only systematized.
Use of a data content includes not only referring to its contents but also normally effectively using by storing, copying, or editing obtained data person via on-line basis by a communication line or via off-line basis using a proper recording medium. Furthermore, it is possible to transmit the edited data content to the database to be registered as new data content.
In a conventional database system, only character data content is handled. In a multimedia system, however, audio data content and picture data content which are originally analog data contents are digitalized and formed into a database in addition to the data content such as characters which have been formed into a database so far.
Under these circumstances, how to deal with a copyright of data content in a database is a large problem. However, there has not been adequate copyright management means for solving the problem so far, particularly copyright management means completed for secondary utilization such as copying, editing, or transferring of the data content.
The inventor of the present invention proposed a system for managing a copyright by obtaining a permit key from a key control center via a public telephone line in Japanese Patent Laid-Open No. 46419/1994 (GB 2269302A) and Japanese Patent Laid-Open No. 141004/1994 (U.S. Pat. No. 5,504,933) and moreover, proposed an apparatus for managing the copyright in Japanese Patent Laid-Open No. 132916/1994 (GB 2272822A).
Moreover, a copyright management method for primary utilization of digital data content such as display (including process to sound) or storage including real-time transmission of the digital data content in a database system and secondary utilization of the digital data content such as copying, editing, or transferring of the digital data content by further developing the above invention is proposed in Japanese Patent Application No. 64889/1994 (U.S. patent application Ser. No. 08/416,037).
The database copyright management system of the above application in order to manage the copyright, either one or more of a program for managing the copyright, copyright information, and a copyright control message are used in addition to a use permit key corresponding to a requested use, and data content which has been transferred with encryption is decrypted to be used for viewing and editing, and the data content is encrypted again when used for storing, copying and transferring.
The copyright control message is displayed when utilization beyond the range of the user""s request or authorized operation is found to give caution or warning to a user and the copyright management program performs monitoring and managing so that utilization beyond the range of the user""s request or authorized operation is not performed.
On the other hand, it is widely practiced to establish LAN (Local Area Network) by connecting computers with each other in offices, organizations, companies, etc. Also, a plurality of networks are connected with each other, and Internet is now organized in a global scale, by which a plurality of networks are utilized as if they are a single network.
In LAN used in an organization such as firms, secret information is often stored, which must not be disclosed to outsiders. For this reason, it is necessary to arrange the secret information in such a manner that only a specific group of users can gain access and use such information, and such access is generally placed under control to prevent leakage of secret information to outsiders.
There are roughly two methods to control the access: a method to control access with access permission, and a method to do it by encryption.
The method of access control by access permission is described in U.S. Pat. Nos. 5,173,939, 5,220,604, 5,224,163, 5,315,657, 5,414,772 and 5,438,508, in EP506435, and in JP Laid-Open 169540/1987.
The access control method based on encryption is disclosed in U.S. Pat. Nos. 4,736,422, 5,224,163, 5,400,403, 5,457,746, and 5,584,023, in EP 438154 and EP 506435, and in JP Laid-Open 145923/1993. The access control method based on encryption and digital signature is described in U.S. Pat. Nos. 4,919,545 and 5,465,299.
Intranet is now being propagated, in which a plurality of LANs are connected with each other via Internet and these LANs are utilized as if they are a single LAN. In the intranet, information exchange is performed via Internet, which basically provides no guarantee for prevention of piracy, and information is encrypted to prevent the piracy when secret information is exchanged.
The prevention of information piracy during transmission by means of encryption is disclosed in U.S. Pat. Nos. 5,504,818 and 5,515,441, and the use of a plurality of crypt keys is described in U.S. Pat. Nos. 5,504,816; 5,353,351, 5,475,757, and 5,381,480. Also, performing re-encryption is described in U.S. Pat. No. 5,479,514.
When encrypting, management of crypt key including transfer and receipt of crypt key becomes an important issue. Generation of keys by IC card is disclosed in U.S. Pat. No. 5,577,121, and encryption/decryption by IC card is disclosed in U.S. Pat. Nos. 5,347,581 and 5,504,817. Also, electronic watermark technique is described in EP 649074.
In the video conference system, a television picture has been added to the conventional voice telephone set. Recently, the video conference system is advanced in which a computer system is incorporated in the video conference system so that the quality of the voice and the picture are improved, and data content can be handled at the same time as well as the voice and the picture.
Under these circumstances, security against the violation of the user""s privacy and the data content leakage due to eavesdropping by persons other than the participants of the conference are protected by the cryptosystem using a secret-key.
However, since the conference content obtained by the participants themselves are decrypted, in the case where participants themselves store the content of the conference and sometimes edit the content, and further, use for secondary usage such as distribution to the persons other than the participants of the conference, the privacy of other participants of the video conference and data content security remains unprotected.
In particular, the compression technology of the transfer of data content is advanced while the volume of the data content storage medium is advanced with the result that the possibility is getting more and more realistic that all the content of the video conference may be copied to the data content storage medium or transmitted via a network.
Also, electronic commerce system with digital data content for commercial dealing is now being used for practical applications. Above all, various types of experiments are now under way for digital cash system to exchange electronic data content instead of cash so that the system can be used by general public.
The digital cash system which has been proposed so far is based on a secret-key cryptosystem. The encrypted digital cash data content is transferred from a bank account or a cash service of a credit company, and is stored in an IC card so that a terminal device for input/output is used to make a payment. The digital cash system which uses this IC card as a cash-box can be used at any place such as shops or the like as long as the input/output terminal is installed. However, the system cannot be used at places such as homes or the like where no input/output terminal is installed.
Since the digital cash is an encrypted data content, any device can be used as the cash-box which stores digital cash data content, in addition to the IC card, as long as the device can store encrypted data content and transmit the data content to the party to which the payment is made. As a terminal which can be specifically used as the cash-box, there are personal computers, intelligent television sets, portable telephone sets such as personal digital assistant (PDA), personal handyphone system (PHS), intelligent telephone sets, and PC cards or the like which has an input/output function.
It is desirable that the digital cash is processed as an object associated with data content and functions instead of being as a simple data content. In handling a digital cash, there are a common digital cash form, an unentered digital cash form private for an owner, an entry column in the digital cash form private for the owner, a digital cash data content showing an amount of money, an instruction of handling digital cash, and a digital cash form private for the owner in which an amount of money is entered. In an object-oriented programming, concepts such as an object, a class, a slot, a message and an instance are used.
In these correspondence relations, the common digital cash form is the object; the unentered digital cash form private for an owner: the class; the entry column of a digital cash form private for the owner: the slot; the instruction of handling digital cash: the message; and the digital cash form private for the owner in which an amount of money is entered: the instance.
A digital cash data content comprising the amount of money and the like is used as an argument, then, is transferred and stored in the slot which is referred to as an instance variable by the message so that a new instance is made which is a digital cash in which the amount of money is renewed.
The encryption technique used in the data management system is utilized not only in the distribution of copyrighted data content but also in the distribution of digital cash.
Then, basic encryption-related technique used in the present invention is described below.
Crypt Key
Secret-key system is also called xe2x80x9ccommon key systemxe2x80x9d because the same key is used for encryption and decryption, and because it is necessary to keep the key in secret, it is also called xe2x80x9csecret-key system.xe2x80x9d Typical examples of encryption algorithm using secret-key are: DES (Data Encryption Standard) system of National Bureau of Standards, FEAL (Fast Encryption Algorithm) system of NTT, and MISTY system of Mitsubishi Electric Corp. In the embodiments described below, the secret-key is referred as xe2x80x9cKsxe2x80x9d.
In contrast, the public-key system is a cryptosystem using a public-key being made public and a private-key, which is maintained in secret to those other than the owner of the key. One key is used for encryption and the other key is used for decryption. Typical example is RSA public-key system. In the embodiments described below, the public-key is referred as xe2x80x9cKbxe2x80x9d, and the private-key is referred as xe2x80x9cKvxe2x80x9d.
Here, the operation to encrypt data content, a plain text material M to a cryptogram Cks using a secret-key Ks is expressed as:
Cks=E(M, Ks). 
The operation to decrypt the cryptogram Cks to the plain text data content M using a crypt key Ks is expressed as:
M=D(Cks, Ks). 
Also, the operation to encrypt the plain text data content M to a cryptogram Ckb using a public key Kb is expressed as:
Ckb=E(M, Kb). 
The operation to decrypt the cryptogram Ckb to the plain text data content M using a private-key Kv is expressed as:
M=D(Ckv, Kv). 
The operation to encrypt the plain text data content M to a cryptogram Ckv using a private-key Kv is expressed as:
Ckv=E(M, Kv), 
and the operation to decrypt the cryptogram Ckv to the plain text data content M using the public-key Kb is expressed as:
M=D(Ckb, Kb). 
The encryption technique is the means to exclude illegitimate use of data content, but perfect operation is not guaranteed. Thus, the possibility of illegitimate use of data content cannot be completely excluded.
On the other hand, electronic watermark technique cannot exclude the possibility of illegitimate use, but if illegitimate use is detected, it is possible to check the illegitimate use by verifying the content of electronic watermark, and there are a number of methods in this technique. These methods are described in Nikkei Electronics, No. 683, 1997-2-24, pp. 99-124, xe2x80x9cxe2x80x98Digital watermarkxe2x80x99 to help stop to use illegal proprietary digital works in the multimedia age.xe2x80x9d Also, description is given on this technique by Walter Bender et al., xe2x80x9cIntroducing data-hiding technology to support digital watermark for protecting copyrights,xe2x80x9d IBM System Journal, vol. 35, Nos. 3 and 4, International Business Machines Corporation.
To prevent piracy or leakage of data content, a cryptography technique and electronic watermark technique are combined together and used. In a data content supplied to a first user, a first user data is entered as electronic watermark by a data management center, and the data content with an electronic watermark entered in it is encrypted using a crypt key and is supplied. The encrypted data content is decrypted using a crypt key distributed from the data management center and is used. In case it is to be stored, it is encrypted using another crypt key.
In case the data content is copied and transferred to a second user, a user data of the second user is entered as electronic watermark, and a scenario to enter the user data of the second user as electronic watermark is registered at the data management center, and the data content with electronic watermark entered in it is encrypted using another crypt key and is supplied. When the validity of the second user is confirmed by the scenario, another crypt key is distributed to the second user. The encrypted data content is decrypted using another crypt key and is used. When it is to be stored, it is encrypted using still another key.
In the data content obtained by the first user, the first user data is entered as electronic watermark by a data center. If the data content is copied and transferred without taking a normal procedure, the data center verifies the electronic watermark entered there, and it is possible to detect that the first user has copied and transferred the data content without taking a normal procedure.
When it is copied and transferred by a normal procedure, electronic watermark of each user is entered, and this makes it possible to clearly define the route of copying and transfer. When copying and transfer are repeated, noise in the data content is increased by the entered electronic watermark, and this makes it possible to exclude and inhibit copying and transfer, i.e. to decrease the risk of illegitimate utilization of data content.
Because a key used for encryption of the data content is stored at the key center, the key center can be utilized when a key escrow system or a key recovery system is used in a practical application.
Further, the secret-key can be used as user data and the secret-key is encrypted using the public-key of the data center and this is entered as electronic watermark. By decrypting this using the private-key of the data center when necessary and by confirming the secret-key, it is possible to achieve a key escrow system or a key recovery system in simple manner but with high security.
In addition to copyright management of data content using a charged crypt key, the present invention is also applicable in applications such as maintenance of privacy of participants in a video conference based on a video conference system using a free-of-charge crypt key and also for maintenance of security of the data content, or the maintenance of data security in electronic data interchange (EDI) such as electronic commerce.